1. Field of the Invention
The invention relates to a fuel cell and a method of controlling the same.
2. Description of the Related Art
A fuel cell constructed by laminating a plurality of single cells each having a membrane electrode assembly (hereinafter referred to as the MEA) interposed between two separators has been known. The MEA is composed of an electrolytic membrane and gas diffusion electrodes. Platinum as catalytic electrodes is applied to both surfaces of the electrolytic membrane, which is interposed between the gas diffusion electrodes. The catalytic electrode and the gas diffusion electrode formed on one surface of the MEA constitutes an anode, and the catalytic electrode and the gas diffusion electrode formed on the other surface of the MEA constitute a cathode. A fuel gas passage in which hydrogen gas as fuel gas to flows through a single cell of the fuel cell is formed in a separator facing the anode. An oxidative gas passage in which air as oxidative gas to flows through the single cell is formed in a separator facing the cathode.
This electrolytic membrane usually functions as a good proton-conductive electrolyte in a wet state and thus is held wet by supplying fuel gas and oxidative gas that have been humidified in advance. However, for various reasons, flooding (a state of being too wet) may be caused. For example, if flooding occurs, water is produced in the gas passage and constitutes a flow resistance against gas, which may make it impossible to supply the gas diffusion electrodes with a sufficient amount of gas. In consideration of this drawback, Japanese Laid-Open Patent Application No. 7-2353234 or the like discloses a fuel cell wherein a dynamic pressure of gas is temporarily increased in response to the occurrence of flooding and wherein produced water in a gas passage is blown off and removed by the dynamic pressure.
However, the fuel cell of the aforementioned publication is designed to cause gas to constantly flow in a certain direction. Hence, if there is some factor (e.g., an obstacle) preventing produced water from moving in the direction, the produced water cannot be easily removed even in the case of an increase in the dynamic pressure of reactive gas.